A large variety of products useful, for instance, as non-ionic surfactants, wetting and emulsifying agents, solvents and chemical intermediates are prepared by the addition reaction (alkoxylation reaction) of alkylene oxides (epoxides) with organic compounds having one or more active hydrogen atoms.
For example, alcohol ethoxylates may be prepared by the reaction of ethylene oxide with aliphatic alcohols of 6 to 30 carbon atoms. Such ethoxylates, and to a lesser extent the corresponding propoxylates and compounds containing mixed oxyethylene and oxypropylene groups, are widely employed as non-ionic detergent components in cleaning and personal care formulations.
US 2008/0167215 A1 discloses specific acylated alcohol alkoxylates for use as low-foam surfactants.
Sulphated alcohol alkoxylates have a wide variety of uses as well, especially as anionic surfactants. Sulphated higher secondary alcohol ethoxylates (SAES) offer comparable properties in bulk applications relative to anionic surfactants such as linear alkyl benzene sulphonates and primary alcohol ethoxy sulphates, as well as methyl ester sulphonates. These materials may be used to produce household detergents including laundry powders, laundry liquids, dishwashing liquids and other household cleaners, as well as lubricants and personal care compositions and as surfactants for (dilute) surfactant flooding of oil wells and as surfactant components used in e.g. alkali, surfactants and polymer containing mixtures, suitable for enhanced oil recovery.
One typical method of preparing alkoxylated alcohols, for example linear or branched primary alcohol alkoxylates, is by hydroformylating an olefin into an oxo-alcohol, followed by alkoxylation of the resulting alcohol by reaction with a suitable alkylene oxide such as ethylene oxide or propylene oxide. However, methods involving hydroformylation are expensive and hydroformylation gives rise to linear or branched primary alcohols (depending on the kind of oxo-reaction) which are to be alkoxylated subsequently.
For some applications, mixtures of secondary alcohol alkoxylates may give improved performance (for example in enhanced oil recovery (EOR) applications in relation to oil solubility).
Secondary alcohol alkoxylates are generally prepared by oxidation/hydroxylation of paraffins, e.g. by the Bashkirov reaction, followed by an alkoxylation reaction.
However, the oxidation of paraffins to secondary alcohols and their subsequent alkoxylation typically involves a complicated two-step process and is hence, an expensive route.
Said process comprises producing secondary alcohols directly from paraffins by oxidation using boric acid as a catalyst. Strictly speaking, the boron reagent is not a catalyst as it is consumed in the reaction. Its function is to protect the oxygenate (sec-alcohol) by reaction to give an oxidation-resistant borate ester. In the overall process including boric acid recycles the boric acid does act as a “catalyst” because its secondary function is to increase the oxidation rate. The borate esters of the secondary alcohols are formed and may be separated from the paraffins by distillation when the carbon number (number of carbon atoms in the alcohol chain) of the alcohol is 14 or less. However, when the carbon number is 15 or more, the distillation temperature required is equal to or above the decomposition temperature of the borate ester and therefore conventional distillation techniques may not be effective.
Furthermore, the oxidation of paraffins in the presence of boric acid derivatives leads to the formation of diols as one of the main by-products (see N. Kurata and K. Koshida, Hydrocarbon Processing, 1978, 57(1), 145-151 and N. J. Stevens and J. R. Livingston, Chem. Eng. Progress, 1968, 64(7), 61-66). Therefore one has to expect that only after very complete purification from these contaminating diols will secondary alcohols be suitable for alkoxylation and that the cost of such purification may render the economics of the overall process unviable.
An alternative route to secondary alcohol alkoxylates described in U.S. Pat. No. 6,017,875 A is by the acid-catalysed addition of oligoethylene glycol to internal olefins. However, said route is cumbersome as it also affords di-alkylated oligoalkylene glycols and internal olefin oligomers as by-products. Thus, said route is also costly.
In current industrial practice, secondary alcohol ethoxylates are made by an expensive two-step process. Firstly, two to three ethyleneoxy units are added to the secondary alcohol using (Lewis) acid catalysts to make a primary hydroxyl-containing low molecular weight (low-mol) ethoxylate. Secondly, after removal of the acid catalyst (generally by neutralisation), the desired additional amount of ethyleneoxy units is reacted with the low-molecular weight ethoxylate (predominantly a primary alcohol mixture) using a basic catalyst such as potassium hydroxide. This two-step approach has the advantage that the inevitable by-product of the (Lewis) acid catalysed ethoxylation, 1,4-dioxane, can be removed by efficient flashing or stripping after removal or by neutralisation of the acid catalyst from the low-molecular weight ethoxylate intermediate product before its conversion to the end-product with the desired level of ethoxylation.
However, it would be desirable to develop a simple and cost-effective method to produce secondary alcohol alkoxylates without 1,4-dioxane formation and without the formation of an alkoxylate with a very wide alkoxylate distribution.
In this regard, it should be noted that alkylene oxide addition reactions are known to produce a product mixture of various alkoxylate groups having different numbers of alkylene oxide adducts (oxyalkylene adducts). The adduct number is a factor which in many respects controls the properties of the alkoxylate molecule, and efforts are made to tailor the average adduct number of a product and/or the distribution of adduct numbers within a product to the product's intended service.
Alkoxylate mixtures in which a relatively large proportion of the alkoxylate molecules have a number (n) of alkylene oxide adducts that is within a relatively narrow range of values have been reported in the art as being preferred for use in certain detergent formulations (GB-A-1462134; Research Disclosure No. 194010). Narrow-range alkoxylates are also known to be particularly valuable as chemical intermediates in the synthesis of certain carboxyalkylated alkyl polyethers (U.S. Pat. No. 4,098,818) and of certain alkyl ether sulfates (GB-A-1553561).
Hence, it would be advantageous to devise an alternative method to produce secondary alcohol alkoxylates, and in particular narrow range alcohol alkoxylates, that would not only avoid having to apply hydroformylation but would also avoid having to resort to rather unstable secondary alcohols as intermediates (which may re-form internal olefins).